1. Field of the Invention
The present invention describes the preparation of new polyethers which can be used as lubricants, particularly as gear lubricants.
2. Discussion of the Background
The use of polyethers as lubricants or as an additive in conventional lubricant oils based on mineral oil is known. The state of the art as well as the demands generally made on such lubricants are particularly described in EP-PS 0 064 236. Suitable values for evaluating the quality of a lubricant oil are the viscosity index VI and the friction coefficient determined using a Reichert wear scale. High-quality lubricants are characterized by a high viscosity index, i.e. extensive temperature independence of the viscosity, as well as low friction coefficients. Additional criteria are compatibility with mineral oil, hydrophobic properties, low pour point and high resistance to heat.
According to EP-PS 0 064 236, polyethers which can be used as lubricants are obtained by copolymerization of a tetrahydrofuran with terminal oxiranes in the presence of monofunctional or bifunctional hydroxy compounds. The oxiranes used are long-chain 1,2-epoxyalkanes with 8-26 carbon atoms, which are used either alone or in a mixture with lower alkylene oxide components, such as ethylene, propylene and/or butylene oxide, as comonomers. These long-chain 1,2-epoxyalkanes can be replaced with glycidyl esters of neoalkane carboxylic acid to a certain extent (see Example 7). However, this measure results in a polyether with a significantly worsened viscosity/temperature behavior, as the comparison with a polyether having a similar molecular weight but not containing any glycidyl ester components shows (see Example 1). Glycidyl esters therefore do not represent an adequate substitute for 1,2-epoxyalkanes. The use of the latter group of compounds therefore appears to be essential for the synthesis of polyethers which satisfy the property profile required by EP-PS 0 064 236.
A need continues to exist for new polyethers which demonstrate good lubricant properties.